After the initial drop, the maximum leakage rate per minute for combination vehicles is:

After the initial drop, the maximum leakage rate per minute for combination vehicles is:

• A. 3 psi
• B. 5 psi
• C. 4 psi
• D. 6 psi

Answer: (C)

The test focuses on how well the air brake system holds pressure when not in active use. After the system is pumped up, you’ll see an initial drop in pressure when the brakes are first released—that drop is expected. What matters is the leakage rate from that point on. For combination vehicles, the allowable leakage is four psi per minute. If the pressure falls more than that in a minute, it indicates a leak that needs repair. This value is higher than the single-vehicle limit (which is typically three psi per minute) because the larger, more complex system in combination outfits can show more leakage. So four psi per minute after the initial drop is the standard to determine acceptable vs. excessive leakage.

The test focuses on how well the air brake system holds pressure when not in active use. After the system is pumped up, you’ll see an initial drop in pressure when the brakes are first released—that drop is expected. What matters is the leakage rate from that point on. For combination vehicles, the allowable leakage is four psi per minute. If the pressure falls more than that in a minute, it indicates a leak that needs repair. This value is higher than the single-vehicle limit (which is typically three psi per minute) because the larger, more complex system in combination outfits can show more leakage. So four psi per minute after the initial drop is the standard to determine acceptable vs. excessive leakage.